Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$166.49	9.554%	$182.3965	$182.40	$182.40	$182.40
Purchase #2	$234.30	3.483%	$242.4607	$242.46	$242.45	$242.50
Purchase #3	$126.86	3.441%	$131.2253	$131.23	$131.25	$131.20
Purchase #4	$178.26	4.426%	$186.1498	$186.15	$186.15	$186.10
Purchase #5	$31.93	11.125%	$35.4822	$35.48	$35.50	$35.50
Purchase #6	$239.45	6.159%	$254.1977	$254.20	$254.20	$254.20
Purchase #7	$67.30	6.717%	$71.8205	$71.82	$71.80	$71.80
7 purchase totals =	$1,044.59		$1,103.7327	$1,103.74	$1,103.75	$1,103.70